This image is a collaboration between me and EWilloughby. She and I recently noticed that a lot of people seemed confused about the distinctions between various groups of dinosaurs, so we created this as a simple guide to it. The images are by her, while I created the layout and wrote all of the text.

There are a few dinosaurs that don't fit into any of these groups, such as Eoraptor, which is a primitive saurischian dinosaur that might have not been either a theropod or a sauropodomorph. But at least 95% of dinosaurs, and all of the best-known dinosaurs, fit into one of these groups.

Maybe it's overly pedantic for the purposes of this poster, but aren't "prosauropods" not a thing anymore? Also, I feel like Theropoda is diverse and well-known enough (in the popular consciousness) that it could use another two or three examples, specifically an ornithomimid and Spinosaurus (maybe Allosaurus too). Also I feel like Edmontosaurus belongs on here as the quintessential "duckbill dinosaur" but I'm less upset about that.

Oh, and this is probably overkill, but if this is really meant to educate laypeople about dinosaur classification, including a "not a dinosaur" section with Dimetrodon, Pteranodon, Elasmosaurus, etc. with accompanying text may be useful, since the question "what about ______?" in reference to those is almost inevitably going to come up.

The reason I didn't include more theropods is just because of the space limitation. There was barely enough room for the three I included unless I made the boxes wider, in which case all the other boxes would have had a lot more empty space in them. (Unless I included more dinosaurs in every group, which would have required a lot more work from Emily.)

Making the images for chart already involved more work from her than she really should have had time for, so she wasn't interested in illustrating things that aren't dinosaurs for it. There are a lot of other things we could've included on it, but we had to draw the line somewhere.

She and I discussed back and forth for quite a while about whether to include prosauropods or not. I was initially intending to leave them out because I assumed the group was obsolete, but she pointed out that Google scholar shows 114 results since the beginning of 2013, so it can't be completely obsolete yet. The more relevant factor is that there isn't any other group within Sauropodomorpha that can include Massospondylus, Plateosaurus and Anchisaurus. (Unless you think they're all plateosaurids, in which case Prosauropoda is just another name for Plateosauridae.) I'd like people looking at the chart to be able to understand that dinosaurs like these belong inside Sauropodomorpha, but outside Sauropoda.

Somewhat ironic then that both of the pictured "prosauropods" were probably obligate, not facultative, bipeds! And I realize it's likely for the sake of simplicity, but the description for ceratopsians doesn't quite encompass things like Psittacosaurus.